A potent form of interocular suppression, called continuous flash suppression (CFS), occurs when a dynamic, changing pattern (e.g. a series of Mondrians) flashed continuously to one eye renders an image presented to the other eye undetectable throughout the viewing period. Although the spatiotemporal structure of the two stimuli can influence the depth of interocular suppression (Yang & Blake, 2012), the precise nature of the mechanisms that mediate CFS and the conditions under which it occurs have not been well studied. We sought to investigate if CFS depends on the relative contrasts and mean luminances of the suppressing and supressed stimuli. The suppressing stimulus was dynamic (10 Hz) 2D visual noise presented to one eye and the probe stimulus presented to the other eye was a horizontal sinusoidal grating (1.8 c/°) that underwent a smooth temporal contrast increment in either the top or bottom half of the display. Observers (N = 8) judged the probe location and increment thresholds were measured using an adaptive staircase for each of a range of dynamic noise contrasts (0 to 0.8), grating pedestal contrasts (0 to 0.4) and interocular differences in mean luminance (ratio 1 to 0.06). Results showed that the depth of interocular suppression due to CFS increased strongly (by up to a factor of ~ 25) with the contrast of the dynamic noise. The threshold versus noise contrast function was characterised by a straight line on linear-log axes. The slope of this line (an index of suppression gain) differed markedly between observers but was affected little by the pedestal contrast of the grating. Systematically reducing the mean luminance of the dynamic noise relative to the grating progressively reduced the measured suppression. Thus CFS is not an all-or-nothing phenomenon and its potency depends critically both on low-level stimulus properties (e.g. contrast and luminance) and the individual observer.